Probing transforms set-up and measurement routines

Citation

(2001), "Probing transforms set-up and measurement routines", Aircraft Engineering and Aerospace Technology, Vol. 73 No. 6. https://doi.org/10.1108/aeat.2001.12773fab.003

Probing transforms set-up and measurement routines

Probing transforms set-up and measurement routines

Keywords: Heidenhain, Probes

It is reported that the introduction of Heidenhain probes has had a major impact on production efficiency at the Dorset, UK, works of Professional Welding Services (PWS) by saving between four and five hours from inspection processes, reducing lead times by some 15 per cent and reducing cutting tool setting time from hours to minutes (see Plate 4).

Plate 4 The retrofitting of Heidenhain probes has reduced setting times from hours to minutes at Professional Welding Services

Specialising in the sub-contract machining of precision components for the aerospace and defence sectors, the Wimborne-based company informs us that it has nothing but praise for the four retrofitted Heidenhain TT 120 table probes and four TS 630 infrared touch trigger spindle probes that have been retrofitted to Bridgeport vertical machining centres. These were installed by Heidenhain's distributor for southern England, Engineering Equipment Centre of Bournemouth.

"The use of Heidenhain table mounted tool probes has enabled us to reduce tool setting cycles from at least one hour to just five minutes on each Bridgeport", says production manager, Chris Reed. He then adds: "On inspection we are typically saving around four to five hours on complex parts through the in-process measurement of key features using the Heidenhain spindle probe, as opposed to checking components offline on a co-ordinate measuring machine (CMM)".

Describing further advantages he says: "Combined with faster datuming, probing has helped cut our lead times by up to 15 per cent. Also, confidence on the shopfloor has improved, as operators no longer have to be so concerned about setting-up and the probes have also simplified inspection and general SPC routines".

Established some 15 years ago, PWS provides a complete sub-contract service covering sheet metalwork and fabrication which now accounts for about half of the business. Precision machining takes a further third and welding the rest. The company is involved in a number of major aerospace projects including: a midlife upgrade for the GR4 Tornado and several contracts for the Eurofighter including drop tank skins and ancillaries.

PWS has invested some £500,000 on new CNC machine tools and CAD/CAM equipment over the last two years. As part of the investment, four Bridgeport 760/22 vertical machining centres fitted with Heidenhain TNC controls were installed in the 12,000ft² factory on the Ferndown Industrial Estate.

To optimise efficiency on its new machines, the company decided to introduce probing routines for tool setting, component datuming and the in-process measurement of key features on airframe components. This was driven by the new contracts and was seen as a general move to streamline setting and inspection routines.

One problem, however, was the short timescale involved, so the probing situation had to be resolved quickly, as Chris Reed describes: "While several suppliers were contacted, Heidenhain was the only one which responded promptly and promised to supply the necessary table and spindle probes to meet our tight deadline. Both Heidenhain and its distributor Engineering Equipment Centre pulled out all the stops to help us and the eight probes were retrofitted and all in production in less than five working days".

Important for PWS is that tool setting procedures have now been automated using the Heidenhain table-mounted TT120 probes. A special routine has been written which cycles through all the 21 tools loaded in the automatic toolchanger, which keeps one position reserved for the spindle probe. The macro automatically brings each tool in turn to contact the disc of the probe, which then feeds cutter radius and length data directly back to the TNC control. This routine reportedly takes just five minutes and is performed without any operator involvement. The machine is then ready to start cutting and each tool is probed once again just prior to being introduced to the component for final data qualification.

Virtually all the Bridgeport set-ups are now probed for datum setting using the Heidenhain TS 630 infrared spindle probes. On a simple job this is said to take less than a minute, while more complex components, involving say 25 position checks, can take up to three minutes. Once again automated routines for these tasks have also been written.

With fairly small batch sizes, say typically between 15 and 20 parts, several different set-ups are often required on each machine during the week. Materials machined include aircraft steels, titanium, aluminium alloy and nimonics and component sizes range from 50mm³ up to 750mm by 500mm by 250mm. General tolerances are around 0.10mm.

As well as datum setting, the TS spindle probe is also used to confirm that the part is actually loaded the right way round, however, its main function is to provide an in-process measuring capability. Key component features to be checked are bores, hole positions, pocket depths and wall thicknesses.

The probe is loaded from the tool changer and all measured results are transmitted to the machine's TNC control and then downloaded to a PC which is used to generate first article reports and provide SPC data. The Bridgeports are regularly inspected for positional accuracy using laser and ballbar techniques while selected components are double-checked on a CMM to verify the measured results.

A particular Tornado aircraft component is an S98 steel bracket. Required in batches of 20, these 254mm long by 76.2mm wide by 50.8mm deep parts are machined from a solid billet. The brackets are roughed and finished in a cycle that involves four rectangular pockets to different depths and with varying wall thicknesses. A 1.5° taper is required on the back face with profiling on the sloping dividers between the pockets. Some 15 small holes also have to be produced.

The total machining time is 90 minutes. "Probing, which includes datum setting and the measuring of 19 points to verify key features, takes just three minutes to carry out", says Chris Reed.

A totally different scale component is a large main spar for an underwing avionics pod. Machined from solid billets of L168 aluminium alloy, in batches of eight, these spars measure some 1,780mm long by 203mm wide by 127mm deep. Machining is set around two separate stages on the Bridgeport due to the length of the part with re-positioning part-way through the cutting cycle. By using the TS 630 spindle probe, the correct datum is easily picked up and the cycle resumed after the spar has been moved along.

Main features on the underwing spars include eight large pockets on the front face and eight smaller pockets on each of the two sides. Both the front and rear faces have two-dimensional curved surfaces which involve extensive 3-D milling. Two 76mm bores in the front face and a large number of small drilled and tapped holes also have to be produced which, in total, takes around 200 hours per part.

Chris Reed outlines how the Heidenhain probes save an enormous amount of time as each of the four faces has to be machined individually, involving eight separate set-ups. "Even so", he says, "datum setting routines only take about 16 minutes to perform. When this is added to the saving by measuring the finished component on the machine table using the spindle probe, we have totally decimated the previous times for inspection".

Previously, due to the heavy demands on the CMM, it could take up to two days to check the various features such as pocket positions, widths and depths; bore size and position; cut-out section profiles and various wall thicknesses. Says Chris Reed: "Our new on machine method takes just 40 minutes". However, to verify results on such key components, at least one out of every batch is also subjected to a separate inspection routine on the CMM.

Further details are available from Heidenhain (GB) Limited. Tel: +44 (0) 1444 247711.